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| United States Patent |
5,206,279
|
|
Rowland
, et al.
|
April 27, 1993
|
Method of preparing aqueous dispersions of
ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymers
Abstract
Aqueous dispersions of ethylene/.alpha.,.beta.-unsaturated carboxylic acid
interpolymers (e.g., random ethylene/acrylic acid interpolymers) are
formed using a mixture of bases at a concentration of at least about 0.2
equivalents of base per mole of .alpha.,.beta.-unsaturated carboxylic
acid. The dispersions have at least about 10 weight percent dispersed
solids and not more than about 1 weight percent of the initial polymer in
non-dispersed form. Preferred bases for use in forming the dispersions are
ammonium hydroxide and/or alkali metal hydroxides. A mixture of ammonium
hydroxide and potassium hydroxide is especially preferred for forming the
dispersions with ethylene/acrylic acid interpolymers at an ammonium
hydroxide:acrylic acid molar ratio of about 1:1 and a potassium
hydroxide:acrylic acid molar ratio in the range of about 0.6-0.8:1. The
dispersions are particularly useful in forming thin coatings of adhesive
on substrates, such as paper and metal foil, using conventional
techniques.
| Inventors:
|
Rowland; Michael E. (Lake Jackson, TX);
Springs; Kenneth E. (Clute, TX)
|
| Assignee:
|
The Dow Chemical Company (Midland, MI)
|
| Appl. No.:
|
646134 |
| Filed:
|
January 25, 1991 |
| Current U.S. Class: |
524/379; 524/429; 524/522; 524/556; 525/329.9; 525/330.2; 525/369; 525/378; 525/380 |
| Intern'l Class: |
C08K 005/05 |
| Field of Search: |
524/556,522,379,429
525/329.9,330.2,369,378,380
|
References Cited
U.S. Patent Documents
| 3347811 | Oct., 1967 | Bissot | 524/556.
|
| 3389109 | Jun., 1968 | Harmon et al. | 524/556.
|
| 3427280 | Feb., 1969 | Imhof | 524/556.
|
| 3472825 | Oct., 1969 | Walter et al. | 525/330.
|
| 3511799 | May., 1970 | Clampitt | 524/556.
|
| 3541033 | Nov., 1970 | Buttrick | 524/556.
|
| 3644258 | Feb., 1972 | Moore et al. | 524/556.
|
| 3677989 | Jul., 1972 | Jenkinson | 524/556.
|
| 3790521 | Feb., 1974 | McCann et al. | 524/556.
|
| 3798194 | Mar., 1974 | McCann et al. | 524/556.
|
| 3799901 | Mar., 1974 | McCann et al. | 524/556.
|
| 3970626 | Jul., 1976 | Hurst et al. | 524/556.
|
| 4173669 | Nov., 1979 | Ashida et al. | 524/556.
|
| 4410655 | Oct., 1983 | Funakoshi et al. | 524/522.
|
| Foreign Patent Documents |
| 89/07519 | Aug., 1989 | PCT.
| |
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Reddick; J. M.
Claims
What is claimed is:
1. In a method of forming an aqueous dispersion of at least one
ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymer
comprising contacting the interpolymer(s) in a stirred aqueous medium with
a mixture of bases, the improvement characterized by contacting the
interpolymer with at least about 0.2 equivalents of base per mole of
.alpha.,.beta.-unsaturated carboxylic acid, said base being a mixture of
monoethanolamine, diethanolamine or ammonium hydroxide and at least one
alkali metal hydroxide in a ratio of from about 1.5 to about 3 moles of
ammonium hydroxide per mole of alkali metal hydroxide, thereby forming a
dispersion having at least about 10 weight percent of dispersed solids,
total weight basis at not more than about 1 weight percent of
non-dispersibles, based on the weight of the interpolymer.
2. The method of claim 1 wherein the solids content of the dispersion is at
least about 25 weight percent, total weight basis.
3. The method of claim 1 wherein the mixture of base is a mixture of
ammonium hydroxide and at least one alkali met hydroxide.
4. The method of claim 3 wherein the alkali metal hydroxide is lithium
hydroxide, potassium hydroxide or sodium hydroxide.
5. The method of claim 4 wherein the mixture is ammonium hydroxide and
potassium hydroxide.
6. The method of claim 5 wherein the ethylene/.alpha.,.beta.-unsaturated
carboxylic acid interpolymer is an ethylene/acrylic acid interpolymer.
7. The method of claim 6 wherein the mixture of ammonium hydroxide and
potassium hydroxide is at a total ratio of from about 1.5:1 to about 3:1.
8. The method of claim 7 wherein the ammonium hydroxide:acrylic acid molar
ratio is about 1:1 and the potassium hydroxide:acrylic acid molar ratio is
from about 0.6-0.8:1.
9. The method of claim 1 wherein the aqueous medium additionally contains
an alcohol of 1 to 4 carbon atoms.
10. An aqueous dispersion produced by the method of claim 1.
11. Film produced from the dispersion of claim 10.
12. The method of claim 1 wherein the ratio of ammonium
hydroxide:.alpha.,.beta.-unsaturated carboxylic acid molar ratio is about
1:1 and the alkali metal hydroxide:.alpha.,.beta.-unsaturated carboxylic
acid molar ratio is from about 0.6-0.8:1.
13. The method of claim 1 wherein said interpolymer is contacted
sequentially first with one of the alkali metal hydroxides, either in an
aqueous or non-aqueous environment, and then contacted with ammonium
hydroxide or a mixture of ammonium hydroxide and another of the alkali
metal hydroxides in an aqueous medium.
14. The method of claim 1 wherein the ethylene/.alpha.,.beta.-unsaturated
carboxylic acid interpolymer is an ethylene/acrylic acid interpolymer.
Description
FIELD OF THE INVENTION
This invention relates to an improved method of forming aqueous dispersions
from ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymers
(e.g., ethylene/acrylic acid). More particularly, the invention relates to
a method of forming dispersions which have a high solids content and
contain not more than about 1% by weight non-dispersibles.
BACKGROUND OF THE INVENTION
Ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymers are
thermoplastic polymers which are useful as adhesives. An adhesive layer or
coating of the interpolymers can be applied to a substrate, such as paper
or metal foil, by extrusion coating or other conventional techniques. The
coating thickness, however, cannot be reduced much beyond about 0.4 mils,
or about 6 pounds per ream, due primarily to the melt strength of the
interpolymer. The line speed and the die/system design also affect the
ability of the interpolymer to coat the substrate at minimal thicknesses.
Generally, such coatings are thicker than necessary to provide the desired
properties in a laminate structure. Thinner coatings would be preferred
from an economic standpoint.
Thin coatings have been applied to substrates using a gravure or meyer rod
technique and an aqueous dispersion of the polymeric adhesive, but the
dispersions have been only available at low solids concentrations.
Many methods of forming dispersions from
ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymers are
disclosed in the literature. One method involves neutralizing at least
portion of the carboxylic acid groups with an alkaline base to form a
dispersible carboxylic acid salt. The dispersions formed using this
technique, especially when the .alpha.,.beta.-unsaturated carboxylic acid
content is low or the molecular weight of the interpolymer is high,
typically have a high content of non-dispersibles, i.e., greater than 1%.
When such dispersions are coated onto a substrate, the coating tends to be
uneven and variable and, in addition, can contaminate the equipment due to
the high percentage of non-dispersibles. The non-dispersibles gum up the
equipment and cause equipment shutdown and subsequent cleanup. If more
base is utilized to reduce the non-dispersibles content, the percentage of
dispersed solids decreases even further and makes the overall process
uneconomical. Dispersions of interpolymers having low carboxylic acid
content (e.g., less than about 15% acid content) are particularly
difficult to form.
International Patent Application Publication Number WO 89/07519 (Patton et
al.) discloses a number of techniques for forming dispersions from
ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymers,
including using a combination of alkali metal hydroxide and ammonia
solution. Patton et al. did not recognize, nor do they suggest, using a
mixture of bases in the proportions set forth below.
SUMMARY OF THE INVENTION
An improved method of forming a dispersion of at least one
ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymer has now
been discovered. The method comprises contacting the interpolymer in a
stirred aqueous medium with a mixture of bases at a concentration of at
least about 0.2 equivalents of base per mole of .alpha.,.beta.-unsaturated
carboxylic acid, thereby forming novel aqueous dispersions having at least
about 10 weight percent (%) of dispersed solids, total weight basis, and
not more than about 1 weight percent (%) of non-dispersibles, based on the
weight of the interpolymer. The preferred bases are ammonium hydroxide
and/or alkali metal hydroxides. Lithium hydroxide, potassium hydroxide and
sodium hydroxide are preferred alkali metal hydroxides. The solids content
of the dispersion is preferably about 25 weight percent or more, total
weight basis.
The adhesive dispersions formed using the method of the present invention
can surprisingly be coated onto a substrate at a film thickness as thin as
about 0.15 mils (or, when coating paper, about 2.25 pounds per ream) and
possibly even thinner. This coating thickness is very desirable from an
economic standpoint as well as an aesthetic standpoint, especially when
coating cellulosics.
In addition, since the dispersions formed using the method of the present
invention have low percentages of non-dispersibles, they cause less
equipment fouling.
DETAILED DESCRIPTION OF THE INVENTION
Ethylene/.alpha.,.beta.-unsaturated carboxylic acid interpolymers form a
known class of compounds, any one of which can be used in the present
invention. Mixtures of the ethylene/.alpha.,.beta.-unsaturated carboxylic
acid interpolymers are useful within the scope of this invention as well.
The preferred ethylene/.alpha.,.beta.-unsaturated carboxylic acid
interpolymer for use in the present invention, however, is a random
ethylene/acrylic acid interpolymer. For example, PRIMACOR* Adhesive
Polymers made by The Dow Chemical Company are random ethylene/acrylic acid
interpolymers suitable for use in practicing this invention.
The interpolymers useful in this invention are prepared by known
techniques. Typically, such polymers are interpolymers of ethylene and
acrylic or methacrylic acid. Other .alpha.,.beta.-unsaturated carboxylic
acids suitable for interpolymerization with ethylene for use in the
present invention include but are not limited to, e.g., maleic acid and
fumaric acid.
One method of preparing such random interpolymers is disclosed in U.S. Pat.
No. 3,520,861 (Thomson et al.) and another is disclosed in U.S. Pat. No.
4,351,931 (Armitage), both of which are incorporated herein by reference.
Another method is disclosed in U.S. Pat. No. 4,599,392 (McKinney et al.
and in allowed U.S. application Ser. No. 07/316,257, both of which are
incorporated herein by reference. Non-random ethylene
.alpha.,.beta.-unsaturated carboxylic acid interpolymers can be prepared
by the methods disclosed in U.S. Pat. No. 4,248,990 (Pieski et al.) and in
U.S. Pat. No. 4,252,924 (Chatterjee), both of which are incorporated
herein by reference. Other methods of manufacturing interpolymers of
ethylene and .alpha.,.beta.-unsaturated carboxylic acid(s), such as
grafting acrylic acid onto an ethylene polymer or copolymer of ethylene as
disclosed in U.S. Pat. No. 3,177,269, incorporated herein by reference, is
also within the scope of this invention. The term interpolymers used in
describing the present invention includes copolymers and terpolymers
(e.g., ethylene/n-butyl acrylate/acrylic acid) and other interpolymers.
The molecular weight of the random ethylene/acrylic acid interpolymers
useful in forming dispersions in the present invention is indicated as
melt index and can be from about 1 gram/10 minutes (g/10 min) to about
5000 g/10 min. The melt index is measured according to ASTM D 1238
Condition E (190.degree. C./2.16 kg). The preferred melt index range of
the random ethylene/acrylic acid interpolymer is from about 5 g/10 min to
about 300 g/10 min. The methods described herein are particularly
effective for forming dispersions from relatively high molecular weight
interpolymers (i.e., interpolymers having a melt index of from about 1
g/10 minute to about 30 g/10 minute).
Surprisingly, even ethylene/acrylic acid interpolymers having very low
acrylic acid content, as low as about 3% acrylic acid by weight of the
interpolymer, can be dispersed using the methods described herein.
Accordingly, the acrylic acid content of the ethylene/acrylic acid
interpolymers can be from about 3% to about 50% by weight of the
interpolymer. The preferred acrylic acid content range of the random
ethylene/acrylic acid interpolymer is from about 6% to about 20% by weight
of the interpolymer.
In addition, ethylene/acrylic acid interpolymers having either relatively
high molecular weights and/or low acid content can be dispersed using the
methods described herein.
The mixture of bases useful for forming the dispersions of the present
invention can be any that react with the .alpha.,.beta.-unsaturated
carboxylic acid functionality, such as alkali metal hydroxides, amines,
ammonium hydroxide and various carbonates (e.g., calcium carbonate or
sodium carbonate). Amines suitable for practicing the present invention
are, e.g., monoethanolamine and diethanolamine. Preferred bases are
ammonium hydroxide and/or alkali metal hydroxides. Lithium hydroxide,
potassium hydroxide and sodium hydroxide are preferred alkali metal
hydroxides. When ammonium hydroxide is used in the invention for forming
the dispersion, the most preferred alkali metal hydroxide for forming the
mixture is potassium hydroxide. This mixture is effective when mixed at
specific ratios sufficient to disperse the interpolymer, particularly at a
total ratio of from about 1.5:1 to about 3:1, and especially effective
when the ammonium hydroxide:acrylic acid molar ratio is about 1:1 and the
potassium hydroxide:acrylic acid molar ratio is in the range of about
0.6-0.8:1.
The alkali metal hydroxides and/or ammonium hydroxide mixture can be formed
by mixing together in an aqueous medium in-situ and then contacting with
the interpolymer. This in-situ mixing method is preferable to contacting
the interpolymer sequentially. The interpolymer can be contacted
sequentially first with one of the alkali metal hydroxides, either in an
aqueous or non-aqueous environment, and then contacted with another of the
alkali hydroxides (or ammonium hydroxide) in an aqueous medium to form the
aqueous dispersion.
Added surfactants are not required in forming the novel dispersion, but
they can be included along with other conventional additives so long as
they do not affect the stability of the formed dispersion. Typical
additives include, e.g., pigments, antioxidants, defoamers, wetting agents
(e.g., hexanol), and rosin tackifiers (e.g., that disclosed in U.S. Pat.
No. 4,714,728 (Graham et al.), incorporated herein by reference).
Preferably, the mixture of hydroxides and interpolymer are agitated or
otherwise stirred sufficiently such that the hydroxide mixture readily
contacts the interpolymer. The temperature of the stirred
hydroxide/interpolymer mixture (i.e., digestion temperature) can be about
ambient or above, but is preferably from about 60.degree. C. to about
150.degree. C.
The non-dispersibles of the dispersions formed using the methods of the
present invention are characterized by filtering the dispersion through a
100 mesh screen, drying the filtrate and weighing. Percent
non-dispersibles is calculated by dividing the weight of the dried
filtrate by the weight of the total polymer charged to the system
multiplied by 100. The solids content of the dispersions is determined by
removing an aliquot of the dispersion, recording its wet weight and
subsequently drying under heat until the weight change is minimal. The
solids content is recorded as the dry weight of the dispersion aliquot,
after removal of non-dispersibles, divided by the wet weight of the
aliquot, multiplied by 100. In general, as the solids content of the
dispersion increases, the viscosity of the dispersion increases. Practical
high solids dispersions can have a viscosity as high as about 2000
centipoise (cps), although lower viscosity dispersions are preferable.
The aqueous dispersions formed using the present invention can be diluted
with an aqueous alcohol of 1 to 4 carbon atoms (e.g., methanol, ethanol or
isopropanol). The addition of alcohol can speed drying time and
consequently increase line speed.
The dispersions of the present invention can be applied to a variety of
substrates, including, e.g., cellulosics (e.g., paper sizing or coating),
metal foil, metal foil coatings, non-woven fabric coatings and polymeric
film. The dispersions of the present invention can be applied using a
gravure roll or meyer rod application technique, or any other dispersion
application technique commonly employed in the industry.
EXAMPLE 1 AND COMPARATIVE EXAMPLES 2 AND 3
A 27 weight percent acrylic acid copolymer with a melt index of 15 grams/10
minutes is dispersed in various alkaline aqueous metal hydroxide solutions
according to the recipes listed in Table 1. The neutralization level for
all samples (moles acid:moles base) is a constant 2.5.
TABLE 1
______________________________________
Sample Resin NH.sub.4 OH
KOH H.sub.2 O
Number (grams) (grams) (grams)
(grams)
______________________________________
1 10.00 3.72 2.34 83.94
2* 10.00 0.00 5.85 84.15
3* 10.00 6.20 0.00 83.80
______________________________________
*Comparative example only; not an example of the invention
The test samples are each made by directly placing all ingredients in a 150
ml 3 neck round bottom flask fitted with a condenser, a thermometer and an
air driven stirrer. Water is added into the flask first, then the resin.
In sample 1, the KOH is added next and then the NH.sub.4 OH added last and
the flask closed. The continuously stirred samples are heated to
95.degree. C. and held constant. The samples are cooled to 50.degree. C.
and filtered through a tared 100 mesh stainless steel screen. The amount
of material remaining on the screen after rinsing and drying for 24 hours
at 90.degree. C. was termed "non-dispersibles". The percent
non-dispersibles was calculated by dividing the grams of material retained
in the filter by the initial weight of resin added to the flask. The
solids content of the dispersions is obtained by removing an aliquot of
the filtered dispersion, recording its wet weight and subsequently drying
under heat until the weight change is minimal. The solids content is
recorded as the dry weight of the dispersion aliquot after removal of
non-dispersibles, divided by the wet weight of the aliquot, multiplied by
100. The results for the three dispersions prepared according to the above
recipes are tabulated below in Table 2.
TABLE 2
______________________________________
Approximate
Stable Solids
Non-dispersible
Viscosity
Content
Example (weight %) (cps) (weight %)
______________________________________
1 0.32 29 11.5
2* 85.0 10 2.1
3* 64.2 14 3.6
______________________________________
*Comparative example only; not an example of the invention
Non-dispersibles greater than 1.0 percent by weight are excessive and the
dispersion is considered unsuccessful. Viscosity of the dispersion is
determined using a Brookfield viscometer using a #2 spindle after two
weeks aging at room temperature and pressure.
EXAMPLE 4 AND COMPARATIVE EXAMPLES 5 AND 6
An ethylene/acrylic acid interpolymer having about 14.57 percent by weight
acrylic acid and a melt index of 24.04 grams/10 minutes (125.degree.
C./2.16 kg) is dispersed using the recipes described in Table 3. The
neutralization level for all samples is 1.5:1 (moles acid/moles base).
TABLE 3
______________________________________
Resin NH.sub.4 OH
NaOH H.sub.2 O
Example (grams) (grams) (grams)
(grams)
______________________________________
4 10 1.33 0.45 88.22
5* 10 2.00 0.00 88.00
6* 10 0.00 1.35 88.65
______________________________________
*Comparative example only; not an example of the invention
This sample is prepared in a manner analogous to that described above. The
results for this sample are also determined in the aforementioned manner.
The dispersion criteria is the same as above; test results are listed in
Table 4.
TABLE 4
______________________________________
Approximate
Stable Solids
Non-dispersible
Viscosity
Content
Example (weight %) (cps) (weight %)
______________________________________
4 0.04 48 10.3
5* 22.5 21 7.8
6* 32.4 18 7.5
______________________________________
*Comparative example only; not an example of the invention
EXAMPLE 7 AND COMPARATIVE EXAMPLES 8 AND 9
An ethylene/acrylic acid interpolymer having about 15.47 percent by weight
acrylic acid and a melt index of about 20.0 grams/10 minutes (190.degree.
C./2.16 kg) is dispersed according to the recipes described in Table 5.
The ratio of acid to base (moles:moles) is 2.5.
TABLE 5
______________________________________
Resin NH.sub.4 OH
KOH H.sub.2 O
Example (grams) (grams) (grams)
(grams)
______________________________________
7 10 2.13 1.34 86.53
8* 10 3.55 0.00 86.45
9* 10 0.00 3.35 86.65
______________________________________
*Comparative example only; not an example of the invention
Dispersion test results are listed in Table 6.
TABLE 6
______________________________________
Approximate
Stable Solids
Non-dispersible
Viscosity
Content
Example (weight %) (cps) (weight %)
______________________________________
7 0.16 64 10.9
8* 18 22 8.2
9* 23 19 9.5
______________________________________
*Comparative example only; not an example of the invention
EXAMPLE 10 AND COMPARATIVE EXAMPLE 11 AND 12
A 9.80 weight percent acrylic acid copolymer with a melt index of 20.0 at
190.degree. C./2,16 kg is dispersed according to the following recipes.
The molar ratio of acid to base is 2.5:1. This sample is prepared in a
sealed one liter stainless steel reaction kettle at a digestion
temperature of 145.degree. C. Table 7 lists the dispersion formulations
and Table 8 lists the properties of the formed dispersions.
TABLE 7
______________________________________
Resin NH.sub.4 OH
KOH H.sub.2 O
Example (grams) (grams) (grams)
(grams)
______________________________________
10 10 1.28 0.80 87.92
11* 10 2.12 0.00 87.88
12* 10 0.00 2.01 87.99
______________________________________
*Comparative example only; not an example of the invention
TABLE 8
______________________________________
Approximate
Stable Solids
Non-dispersible
Viscosity
Content
Example (weight %) (cps) (weight %)
______________________________________
10 0.4 140 10.5
11* 88 14 1.2
12* 72 22 3.2
______________________________________
*Comparative example only; not an example of the invention
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